September 2020

Turning the Sky Orange and the Lights Off: West Coast Wildfires Diminish Solar Power Generation

Isaac Foote, MJLST Staffer

On September 9th, 2020 social media feeds were taken over by images of the sky above San Francisco.  As if it was a scene out of Bladerunner 2049, the sky turned a remarkable shade of orange due to smoke from forest fires raging across the West Coast. The fires have had a devastating effect on the region; they have burned over five million acres of forest, forced over 500,000 people to evacuate their homes, and killed over 30 people. Further, the combustion of millions of trees has threatened air quality across the United States and has released over 83 million tons of CO2 emissions into the atmosphere. This is more CO2 than power plants in both California and Oregon release in a typical year and is another example of how climate change perpetuates itself.

In addition to CO2, when forests burn they also spew incredible amounts of soot (another name for black carbon) into the atmosphere. This soot can then join together with water vapor to create pyrocumulonimbus clouds in the stratosphere which, in turn, are very effective at absorbing light from the sun. Because carbon absorbs more blue light than red light, these soot clouds caused the ominous coloration of the sky above San Francisco on September 9th.

While most of the focus on forest fire smoke has (rightfully) been around its potential health effects, the absorption effect mentioned above can also have a significant impact on solar power installations. At a micro scale, the impact of forest fire smoke can be intense. One small scale solar installation in Cupertino, California saw a 95% reduction in energy generation on September 9th. Outside of California, a Utah study demonstrated that a single forest fire within 150 miles of a solar array reduced generation by 12.5% over a three day period following the start of the fire.

At the systemic level, California Independent System Operator (California ISO) reported that at times on September 10th statewide solar generation was reduced by ⅓ compared to typical summer levels. While this did not set off rolling blackouts (as California ISO was forced to implement in mid-August), a 33% shock to generation is a worrying sign for the future. After all, this wave of wildfires already resulted in significant strain on the California transmission system independent of solar disruption. California has a 100% clean energy generation target for 2045 (SB 100 (de León, 2018)) and projections estimate solar will need to constitute a large percentage of California’s energy production to meet this goal. While energy planners factor the instability of solar generation into forecasts of energy production, typical state-wide drops of this magnitude usually occur in winter, when energy demand is reduced due to lower temperatures. With the increased prevalence and intensity of forest fires, California grid operators must be wary of sudden smoke-related drops going into the future, especially during the hot and dry weather that corresponds with both forest fires and high energy usage.

According to the Solar Energy Industries Association, “[a] worst-case wildfire scenario could reduce annual solar-energy production from affected installations by as much as 2%.While this impact may seem small on the scale of the energy system, some back of the envelope math estimates this worst-case scenario would reduce California’s annual solar production by 569 gigawatt-hours or $94,340,000 in retail sales at current production levels. This calculation is not even considering additional maintenance costs and efficiency reductions that analysts worry may be necessary if soot settles onto solar panels after leaving the atmosphere.

Of course, none of this is to argue against the increased adoption of solar generation in California. In fact, rapidly moving from a fossil fuel based economy to one based on renewable energy is the most important step in preventing future large forest fires as “the link between climate change and bigger fires is inextricable.” Additionally, advocates of distributed solar argue that increased residential solar adoption may help mitigate the stresses that forest fires place on the electric grid. Instead, this should be treated as another example of the costs of climate change and, consequently, fossil fuel use. Even with aggressive reductions in greenhouse gas emissions, forest fires will continue in the American West and soot will continue to harm solar efficiency. The best solution is for grid operators (like California ISO) and government planners (like the California Energy Commission) to understand the risks forest fires pose to solar generation and factor that into their long term (like the Annual Planning Renewable Net Short) and short term planning processes.